Natural products, especially toxins, have played prominent roles in pharmacology and cell biology due to their potent and selective targeting of specific biochemical pathways and receptors. Marine cyanobacteria and algae are rich in structurally-diverse and biologically-active natural products, and a number are implicated with environmental toxicities. Hence, this continuing collaborative program between a natural products chemist (Gerwick) and a neuropharmacologist (Murray) proposes an integrated investigation of these life forms for their new and biologically-insightful neurotoxins, and has the long range goals of 1) developing new tool compounds for pharmacology and cell biology, 2) describing new putative environmental toxins so that appropriate actions can be taken should outbreaks occur, and 3) development of neurotoxic substances as potential therapeutic lead compounds. To approach these long term goals, we have the following four specific aims in this renewal: Aim 1. To collect, extract, and evaluate for neurotoxic properties the extracts of 200-300 marine algae and cyanobacteria using high throughput screens (FLIPR) with both intact neurons in primary culture and Neuro-2a cells to detect alterations in Ca2+ dynamics and membrane potential; Aim 2. To use contemporary methods to isolate and innovative approaches to structurally characterize new neurotoxic substances from marine algae and cyanobacteria testing positive in the screening assays, featuring MS-MS methods and innovative 2D-NMR spectroscopy; Aim 3. To define the molecular determinants of antillatoxin activation of voltage-gated sodium channel alpha-subunits, kalkitoxin interaction with voltage-gated sodium channel alpha-subunits, and the detailed pharmacological mechanism of action of other newly discovered marine cyanobacterial neurotoxins, including those deriving from specific aims 1 and 2; Aim 4. To produce additional supplies or analogs of newly discovered cyanobacterial and algal neurotoxins, including radioisotope-labeled analogs to be used in radioligand binding assays.